1. Field of the Invention
The present invention relates to an extremely wide angle photographic lens system and more particularly, to a fish eye lens system having a field angle of 180.degree..
2. Description of the Prior Art
The advantages of extremely wide angle lens systems, and more particularly, fish eye lens systems are known in the field of photography. A conventional lens system on a camera will normally provide a limited field angle, which in many cases will prove unsatisfactory to the photographer in attempting to capture the true perspective of what the actual object scene would appear to an observer. Conventional camera bodies, such as the now popular SLR, or single lens reflex camera bodies, are generally adapted to provide a flat focal plane coincidental with the film which places limitations on a complimentarily lens system. The difficulties of utilizing a fish eye lens system to provide a 180.degree. field of angle on an SLR camera are considerable.
As can be appreciated, providing an optimum photographically acceptable aperture ratio, is extremely difficult. With the extreme bending of the light rays in a fish eye lens system, there are considerable problems in compensating for lateral chromatic aberrations, not to mention the large curvature of the field. Additionally, a strong residual amount of astigmatism results from the increased diameter of the front lens element in the fish eye lens system. Another problem with 35 mm. SLR cameras is the position of the reflecting mirror, which requires the fish eye lens system to have a relatively long back focal length.
The Ogura U.S. Pat. No. 3,597,049 provides one example of solving the problem associated with a fish eye lens system by controlling the Abbe values of the lens elements. The Japanese Pat. Nos. 47-23576; and 47-35019 issued in 1972 and the Nakagawa U.S. Pat. No. 3,850,509 are additional examples of fish eye lens systems. The Japanese Pat. No. 39-18718 discloses an achromat fish eye lens system.
The Yamashita, et al U.S. Pat. No. 3,870,400; Zimmerman, et al. U.S. Pat. No. 3,132,199; and the Mukai U.S. Pat. No. 2,969,713 are cited of general interest as simply disclosing wide angle lens systems.
The prior art still has not provided an optimum fish eye lens system that is both photographically acceptable and which can be manufactured relatively inexpensively.